Effects of winter irrigation with heterogeneous water sources on water, salt, and nutrient transport in saline-alkali land

In view of the contradiction between secondary salinization and the shortage of freshwater resources caused by traditional fall irrigation in the irrigation area on the south bank of the Yellow River, this study innovatively proposed the strategy of winter irrigation of aquaculture tail water instead of fall irrigation from the Yellow River. From 2023 to 2024, four treatments, namely, fall irrigation from the Yellow River (S1), winter irrigation from the Yellow River (S2), winter irrigation of aquaculture water (S3), and a control group (CK), were established in Dalate Banner of Ordos for field experiments. Principal component analysis, soil quality index, and nonlinear function model were used to reveal the variation of soil water, salt, and nutrients under these fall irrigation and winter irrigation systems with different water sources. The effects of each treatment were evaluated using SQI index, crop growth status, and principal component analysis of crop soil factors. The results showed that winter irrigation significantly improved soil water retention compared with fall irrigation, and its “ice cap storage” mechanism increased the water content of the soil layer of 40-60 cm in depth to 17.2% (P-1). Compared with the winter irrigation with water from the Yellow River (S2), the organic matter content increased by 2.82 g·kg-1, the ammonium nitrogen increased by 8.73 mg·kg-1, and the nitrate nitrogen increased by 10.53 mg·kg-1. According to the comprehensive evaluation index of soil quality (SQI), the effect of winter irrigation of aquaculture water on soil quality was significantly higher than that of the other treatments. Therefore, according to the actual situation of the irrigation area on the south bank of the Yellow River, salinity of 5-6 g·L-1 and an irrigation amount of 180 mm were selected for winter irrigation of the aquaculture tail water, which could maximize the soil moisture in spring, reduce soil salinity, and improve soil nutrients and overall quality.